Piper SENECA III - Vacuum System

SECTION
7
PIPER
AIRCRAFT
CORPORATION
DESCRIPTION & OPERATION
PA-34-220T,
SENECA
III
7.19
VACUUM
SYSTEM
The
vacuum
system
operates
the air
driven
gyro
instruments.
The
vacuum
system
(Figure
7-17)
consists of
a
vacuum
pump
on
each
engine,
plus
plumbing and
regulating
equipment.
The
vacuum
pumps
are
dry
type
pumps,
which
eliminates
the
need
for
an
air oil
separator
and
its
plumbing.
A
shear
drive
protects
the engine
from
damage.
If the
drive
shears
the
gyros
will
became
inoperative.
The
vacuum
gauge,
mounted
in
the
center
of
the
instrument
panel below
the
radios
(refer
to
Figure
7-21),
provides
valuable
information
to
the
pilot
about
the
operation
of
the
vacuum
system.
A decrease
in
pressure
in
a
system
that
has
remained
constant
over an
extended
period,
may
indicate
a
dirty
filter,
dirty
screens,
possibly
a
sticking
vacuum
regulator
or
leak
in
system
(low
vacuum
indicator lights
are
provided
in
the
annunciator
panel).
Zero
pressure
would
indicate
a
sheared
pump
drive,
defective
pump,
possibly
a
defective
gauge or
collapsed
line.
In
the
event
of
any
gauge
variation
from
the
norm,
the
pilot
should
have
a
mechanic
check the
system
to prevent
possible
damage
to
the
system components
or
eventual
failure
of the
system.
A
vacuum
regulator
is
provided
in
the
system to
protect
the
gyros.
The
valve
is
set
so
the normal
vacuum
reads
4.8
to
5.1
inches
of
mercury, a
setting
which
provides
sufficient
vacuum
to operate
all
the
gyros
at
their
rated
RPM.
Higher settings
will
damage
the
gyros
and
with
a
low
setting
the
gyros
will
be
unreliable.
The
regulator
is located
behind
the
instrument
panet
REPORT: VB-Ill0
ISSUED:
JANUARY
8, 1981
7-22